Studies are proposed which aim to understand the biology of the pancreatic allograft. Inbred strains of rats will receive either a duct-ligated or duct-open pancreatic allograft and the effect of differing histocompatibility, active and passive enhancement, and non-specific immunosuppession on allograft function and survival will be evaluated. In addition, the susceptibility of whole pancreas grafts to humoral immunity in bone marrow and lymph node tolerant rats will be compared to that of isolated pancreatic islets of Langerhans. A spontaneously diabetic rat strain will be used to compare the effect of naturally occurring diabetogenic factors on allografts of whole pancreas and islets. Weak and strong histocompatibilities will be used for all experiments.